Copper(II) carboxylates are known to form complexes with a paddlewheel geometry. When the carboxylate ligands have long chains, the copper(II) dimers often have liquid crystalline mesophases. The melting point of these mesophases varies according to chain length and other structural features such as chain branching and the presence of alkenes. Previous work in our research group revealed that melting points for copper(II) dimer liquid crystals are lowered by carboxylate substitution that produces lower symmetry heteroleptic dimers. It seems likely that packing forces between molecules of the substituted dimers are substantially altered by the reduction in symmetry. The present work utilizes the racemic ligand 2-ethylhexanoate in an attempt to further depress melting points in copper(II) dimer mesogens by introducing both branching and chirality. Our efforts have yielded novel mono, di, and tri substituted copper(II) carboxylate dimers with melting points that approach room temperature. In addition, caprolactam adducts of these compounds were synthesized producing a variety of low melting fluid phases. Characterization included polarized optical microscopy (POM), melting point, differential scanning calorimetry (DSC), elemental analysis, and FT-IR spectroscopy. Our results show 2-ethylhexanoate is a versatile ligand producing copper(II) dimer metallomesogens with surprisingly low melting points and large ranges of mesophase stability.

Synthesis and characterization of thermotropic copper(II) heteroleptic metallomesogens with 2-ethylhexanoate ligands

253rd National Meeting (2017)

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